Lighthouse exposure system providing corrected radiant energy distribution

ABSTRACT

A lighthouse exposure system for more uniformly exposing photosensitive material on a television picture tube face panel. The usual lighthouse problems of (i) over-intense radiation along the face panel parallel to the elongated arc lamp and, (ii) corner-to-corner intensity differential associated with lighthouse light source offset, are both overcome. The intensity contour correcting lenses or shaders (or the like) which are usually disposed between the effective point of light emanation and the face panel are rendered unnecessary. The system employs a light collimator which channels, by means of internal reflection, light from an elongated arc lamp to a collimator tip from which light is then emitted toward the face panel. The surface of the collimator is altered in a predetermined manner so as to interrupt the surface boundary reflection usually occurring therefrom. In a preferred embodiment, the collimator has two frosted areas disposed opposingly and near the tip, with the frosted areas being aligned with the elongated arc lamp.

United States Patent [191 Park 1451 Sept. 24, 1974 LIGHTHOUSE EXPOSURE SYSTEM PROVIDING CORRECTED RADIANT ENERGY DISTRIBUTION [75] Inventor: Yong S. Park, Hanover Park, Ill.

[73] Assignee: Zenith Radio Corporation, Chicago,

Ill.

[22] Filed: July 2, 1973 [21] Appl. No.: 375,587

[52] US. Cl. 354/11 [51] llnt. Cl. G031) 27/00 [58] Field of Search 95/1 R; 354/1; 313/92 B [56] References Cited UNITED STATES PATENTS 2,941,457 6/1960 Weingarten ..'95/1 R 3,452,655 7/1969 Levin et al. 95/1 R Primary ExaminerRichard M. Sheer Attorney, Agent, or Firm-John H. Coult [57] ABSTRACT A lighthouse exposure system for more uniformly exposing photosensitive material on a television picture tube face panel. The usual lighthouse problems of (i) over-intense radiation along the face panel parallel to the elongated arc lamp and, (ii) corner-to-comer intensity differential associated with lighthouse light source offset, are both overcome. The intensity contour correcting lenses or shaders (or the like) which are usually disposed between the effective point of light emanation and the face panel are rendered unnecessary. The system employs a light collimator which channels, by means of internal reflection, light from an elongated arc lamp to a collimator tip from which light is then emitted toward the face panel. The surface of the collimator is altered in a predetermined manner so as to interrupt the surface boundary reflection usually occurring therefrom. In a preferred embodiment, the collimator has two frosted areas disposed opposingly and near the tip, with the frosted areas being aligned with the elongated arc lamp.

10 Claims, 9 Drawing Figures ass-38,432

SHEHZN 2 PRIOR ART PRIOR ART PRIOR ART COLL/MATCH m m W w N 0 c ARC LAMP HR'EAS WHICH /N7'ERRL/PT THE USUHL SURFACE REFLECT/ONS m m M L L 0 C w n a mu W LIGHTHOUSE EXPOSURE SYSTEM PROVIDING (IORRECTED RADIANT ENERGY DISTRIBUTION BACKGROUND OF THE INVENTION This invention relates to the manufacture of color cathode ray tubes. More specifically, it relates to the lighthouse exposure system used in screening the tubes.

In the manufacture of color cathode ray tubes luminescent phosphor targets (often in conjunction with interspersed light absorbing materials) are deposited directly on the tube face panel by means of photographic techniques. For example, if the tube is of the dark surround variety, the image area of the tube is covered with a photosensitive resist material in which light absorptive material is carried in suspension. An apertured shadow mask is then joined with the face panel and this subassembly is mounted horizontally in a lighthouse. Included in the lighthouse is a light source which emits actinic energy in a direction substantially transverse to the panel/mask assembly. The coated screen is exposed three times with each exposure being made through the shadow mask and with the light source each time repositioned slightly off the tube axis to simulate one of the three electron guns of the tube. Developing lays bare the exposed areas; only the unexposed black surround material remains.

As is also well-known in the art, the various color phosphor materials are next applied in a manner analogous to that above. More specifically, a particular color phosphor, suspended in photoresist is applied to the image area whereupon the screen is exposed through the mask from the light source positioned off axis to simulate the electron gun assigned to excite the particular phosphor in process. After developing, elemental areas of this particular phosphor remain and the steps are repeated with each of the other color phosphors to achieve the final screen having many small luminescent phosphor targets.

This heavy reliance on photographic techniques demands a high degree of precision and predictability during the process. Color fidelity in images reproduced by devices utilizing targets of this type is dependent in large measure upon the consistency in configuration and dimensional accuracy of the individual target areas and their positions with respect to one another. The individual target areas are extremely small; for example, there may be more than 750,000 individual target areas inthe screen of a large screen color picture tube. Consequently, the techniques and processes used to fabricate these targets must permit the maintenance of extremely precise dimensional tolerances.

One factor which determines the achievable accuracy and consistency is the light used in exposing the screen andthe uniformity of light intensity. Since elemental phosphor target configuration depends ultimately on a time integration of the light flux impinging on the exposed areas, it is understandable that a uniform light intensity distribution on the screen is desirable not only to simplify exposure processes but to help assure a more uniform elemental phosphor configuration.

A particular problem of light distribution arises as a result of the light source commonly used in lighthouses. The usual source is intended to simulate a point source of high intensity light and conventionally comprises the non-polished tip of a light conducting collimator fabricated of quartz or pyrex. Most often the collimator is substantially bullet-shaped, has a flat end opposite the tip, and is disposed with its major orlongitudinal axis vertically positioned but radially offset from the vertical tube axis to simulate actual gun positioning. A high intensity are lamp, cylindrical and horizontally disposed, is mounted adjacent the flat end of the collimator. Typically an apertured barrier surrounds the collimator tip to assure that only the light departing from the tip arrives at the target. Light from the arc lamp en ters the collimator at the flat end and travels to the tip either directly or by reflection from the collimator surface boundary.

As a result of the cylindrical shape of the arc lamp, the light emitted from the tip is not uniformly intense but produces hot spots on the surface of the image screen substantially parallel to the cylindrical lamp horizontal axis. If an observer moved around a circle located in a plane perpendicular to the collimator longi tudinal axis and whose center were located on the collimator longitudinal axis, the observer would view substantial light intensity variations. In fact, the observer would view more intense light radiation along the circle diameter parallel to the lamp axis than along the transverse diameter. Evidently, these hot spots result in non-uniform exposure patterns. In the prior art, correcting lenses and graded absorptive filters have been used to solve this problem of non-uniform exposure. Furthermore, radial offset of the collimator causes a corner-to-corner differential in light intensity which has heretofore been corrected by various devices such as partial masks, shaders, and lenses. These methods are expensive and difficult to make whereas the present invention provides controlled patterns of illumination with an easily achieved and inexpensive modification of a lighthouse collimator.

It is, therefore, an object of this invention to provide an improved apparatus for manufacturing screen face panels for color television picture tubes. It is another object of the invention to provide apparatus for more uniformly exposing the target surface of a cathode ray tube.

SUMMARY OF THE INVENTION Briefly, in accordance with the invention, a lighthouse exposure system more uniformly exposes photosensitive material on a television picture tube face panel using a panel irradiating source whose panel impinging contours of constant intensity light, if uncorrected, are improperly configured. The system provides on the face panel corrected contours of constant light intensity without the need for light intensity contour correcting devices disposed between the source and the face panel. The system includes means for supporting the face panel, an elongated source of actinic light energy, and a collimator for focusing the light to a simulated point source from which light is transmitted toward the face panel. The system also includes means for correcting the constant intensity light contours impressed on the face panel. The correcting means consist of one or more predetermined non-reflective surface areas on the collimator which are in predetermined alignment with the elongated light source.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects, features and advantages will become more readily understood from the following detailed description taken in connection with the appended claims and attached drawings in which:

FIG. I is an elevational view, partly in section, of a photographic lighthouse having an optical system in accordance with the invention;

FIG. 1A is a sectional view taken along lines lA-lA of FIG. 1 detailing a collimator alignment apparatus;

FIG. 2 is an enlarged view of portions of the collimator, light shield, and arc lamp of the lighthouse of FIG.

FIG. 3 is a side view of the collimator and lamp of FIG. 2;

FIG. 4 is a plan view of the collimator and are lamp of FIGS. 2 and 3;

FIG. 5 represents an idealized light distribution pattern produced on a target surface with a conventional collimator; and

FIGS. 6a, 6b and 6c schematically represent the principle of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, there is shown a specific embodiment of the invention and its relationship to the imaging surface and lamp source in a conventional lighthouse. Other details such as grading filters, shader plates, cooling or adjusting mechanisms are not pertinent to the invention herein and are not shown. The face panel 11, cojoined with aperture mask 12 usually by means of mounting springs 13, rests horizontally atop enclosure funnel 14 on shelf 15 and is laterally disposed to achieve center registry with the funnel reference axis CC. A photosensitive coating 18 adheres to the target surface 19 of the face panel.

The lighthouse optical system includes the usual elongated lamp l6 and associated reflector 17. The system collimator 21, substantially bullet-shaped, is mounted above the lamp such that the optical axis 00 parallels funnel axis CC yet is laterally offset to simulate electron gun position. Appropriate mounting fixtures are provided to secure and align the optical system components. Collimator light shield 23 prohibits all light transmittal from collimator to screen except from the collimator tip 25 which projects through an aperture in the shield.

The particular embodiment of the collimator included in FIG. 1 is illustrated more clearly in FIGS. 2, 3 and 4. The collimator 21 comprises a collimator body portion 27 and a collimator tip 25 disposed atop the collimator body. The upper portion of the bulletshaped collimator body 27 is much like the frustrum of a cone and terminates abruptly at a shelf 29 defined by a plane perpendicular to the collimator optical axis. A

conical collimator tip, its base coincident with the shelf, extends from the shelf along the optical axis and projects through an aperture of collimator body shield 23. The shield masks all stray illumination and enables the tip to simulate a point source of light. A surface boundary discontinuity exists at the shelf thereby creating a shoulder and making the tip base diameter less than shelf diameter. The tip 25 is frosted or roughened or otherwise treated to create light diffusion. The collimator is made of quartz or other appropriate material.

In accordance with the invention, along the collimator body surface adjacent the shelf are small surface areas 31 treated so as to be non-reflective. In the embodiment shown, these areas are configured essentially as inverted triangles and are created by frosting or roughening by sand-blasting the usually smooth collimator body surface. As shown in FIG. 4, each of the frosted areas is bounded by two non-parallel lines projecting downwardly from the shelf 29 along the collimator body surface. The frosting terminates at the intersection of the two lines, i.e., the apex of the inverted triangle. As shown, the third side of the triangle is formed by the perimeter of the shelf. Both triangles are essentially isosceles and are disposed 180 from each other on opposite sides of the collimator body. The collimator is rotationally aligned with arc lamp 16 so that both triangle apexes and the lamp cylindrical axis all lie in the same vertical plane. The alignment may be provided by registry between a boss 41 (see FIGS. 1 and 1A) in the collimator housing 42 and a vertical slot at the rim of the press fitting collimator support collar 43. Other alignment methods will be apparent to those skilled in the art. On a collimator whose body is nominally 1 /2 inches long the height of the triangle shown in FIG. 3 is typically one-fourth inch and included angle alpha ranges typically from to 15.

During normal lighthouse exposure operation without the benefits of this invention, areas of over-intense light radiation, (i.e., hot spots), occur at the imaging surface along an axis parallel to the cylindrical arc lamp axis. Constant intensity contours are elongted or exaggerated along this axis. This is shown more clearly in FIG. 5 which schematically represents the optical system in relation to the imaging surface as both are viewed from above during an exposure step. In FIG. 5, the point N represents the funnel reference axis CC, point G represents the optical axis O-O, axis Z-Z is parrallel to the elongated lamp axis and the degree of relative illumination of the image screen is represented by H (for high) and L (for low). Use of the embodiment of the invention as above-described and as illustrated in FIGS. 1-4 eliminates the areas of over-intense radiation along axis Z-Z, alters the constant intensity contours, and provides, on the image screen, a controlled pattern of light intensity whose constantintensity contours are biased toward circularity. For instance, the variation in light intensity as measured near each of the four corners of a rectangular image screen may be held to a mere 1.5 percent or less.

The results are achieved due to the non-reflective nature of the frosted areas and their location with respect to the cylindrical lamp axis. This may be seen from the explanatory illustrations of FIGS. 6a, 6b and 6c. FIGS. 6a and 6b show that a conventional collimator, at the collimator body zone adjacent the tip, reflects more light in the vertical plane containing the cylindrical lamp axis than in the vertical plane transverse to the lamp axis. By aligning the frosted areas with the lamp axis as shown in FIG. 60, the collimator surface boundary reflections are greatly reduced in the vertical plane containing the lamp. The frosted areas permit some of the light incident thereon to escape and thereby decrease the amount reaching the lamp by reflection from these areas. Of course, the reduced reflection is not confined precisely to a geometrically flat plane, but continues for some angle of rotation about the optical axis depending upon the dimensions of the frosted triangle.

it should be apparent that the above embodiment is designed to overcome a specific illumination problem. The subject matter of the invention is not limited to this embodiment. For example, and as previously mentioned, during lighthouse exposure, the optical axis is radially offset to simulate actual electron gun position. This causes a corner-to-corner light intensity differential due to different exposure angle and distance of light travel. Prior art solutions use correcting lenses or absorption filters between collimator tip and image screen to overcome this exposure problem. Other methods include a partial masking of the tip. The basic principle of the invention herein may be used to provide the same result far more cheaply. By frosting only one side of the collimator body, or, if multiple frosted areas are used, making one frosted area larger than the opposing one, asymmetrical internal reflection is achieved and this with proper alignment of the collimator, compensates for the usual asymmetrical screen illumination or corner-to-corner differential.

The frosted areas may be variously shaped, sized and located, and are not limited to opposingly located triangular configurations. Other geometrically defined areas of anti-reflectivity may be employed. These include parabolic, semi-circular, or cusp-shaped configurations. Continuous annular bands of frosting are a further possibility. Also, a multiplicity of strategically located areas is possible. Additionally, opposing frosted areas may be skewed with respect to one another so that they are not located 180 from each other. Also, although the particular collimator embodiment abovedescribed included a conical collimator tip, the invention may be employed in conjunction with other tip shapes.

it should be further noted that frosting is not the only technique by which reflectivity characteristics of the collimator surface boundary may be changed. Nonreflective or anti-reflective coatings such as magnesium fluoride may be deposited on the surface of the collimator body to achieve much the same effects as the above-described frosting. In general, materials having an index of refraction different from that of air or of the body material may be deposited in appropriate locations on the collimator body surface so that the usual critical angle is changed in these areas, which in turn, changes the reflectivity characteristic of the collimator boundary surface.

Additionally, the reflectivity characteristic may be changed by appropriately altering the curvature of the collimator body surface at locations corresponding to the earlier described frosting. Recalling that the principle of the invention calls for altering the internal reflections from certain portions of the collimator body surface, this may be achieved by a collimator whose body extends or is indented at these locations so that the original area of reflection no longer exists.

From the foregoing, it will be apparent to those skilled in the art that use in a conventional lighthouse of the above-described invention will compensate for improperly configured constant intensity contours. Also as set forth above, use of other more expensive devices to achieve the same end is obviated. Finally, it is apparent that changes and modifications may be made to specific embodiments herein described without departing from the true spirit and scope of the appended claims.

What is claimed is:

1. For more uniformly exposing photosensitive material on a television picture tube face panel using a panel-irradiating source whose uncorrected, panel impinging contours of constant intensity light are improperly configured for picture tube manufacturing purposes, a lighthouse exposure system providing on the face panel corrected contours of constant light intensity without the need for light intensity contour correcting devices disposed between said source and said face panel, said exposure system comprising:

means for supporting a television picture tube face panel;

an elongated source of actinic light energy;

a collimator for focusing the light by reflection from its surface boundary to a simulated point source from which light is transmitted towards said face panel, said collimator having a central optical axis; and

means for correcting the constant intensity light contours impressed on said face panel, said means consisting of:

at least one predetermined non-reflective surface area on the collimator configured to define a noncircular pattern of non-reflectivity about said optical axis so as to affect said light in a manner which varies as a function of rotational angle about said optical axis, and said surface areas having a predetermined angular relationship with respect to said elongated light source.

2. A system in accordance with claim 1, wherein said non-reflective surface areas are sized, shaped, and located to modify the constant intensity light contours toward circularity.

3. A system in accordance with claim ll, wherein said non-reflective surface areas are sized, shaped, and located to reduce the light intensity differentialbetween any two points on the face panel equi-distant and opposingly located from the face panel center.

4i. A system in accordance with claim 1, wherein said non-reflective surface areas are surface-frosted areas.

5. For more uniformly exposing photosensitive material on a television picture tube face panel using a simulated point source of light whose uncorrected, panel impinging contours of constant intensity light are improperly configured for picture tube manufacturing purposes, a lighthouse exposure system providing on the face panel corrected contours of constant light intensity without mechanically modifying the point source physical embodiment, said exposure system comprising:

means for supporting a television picture tube face panel;

an elongated source of actinic light energy;

a collimator for focusing the light by reflection from its surface boundary to a small tip which simulates a point source and transmits light toward said face panel;

a light shield through which only said tip projects and which masks the face panel from all other parts of the collimator; and

. means for correcting the constant intensity light contours impressed on said face panel, said means consisting of:

at least one predetermined non-reflective surface area on the collimator, said areas being located on the collimator portion which is masked from the face panel by said light shield, and said areas being positioned in predetermined alignment with said elongated light source.

6. A system in accordance with claim 5, wherein said non-reflective surface areas are sized, shaped, and located to modify the constant intensity light contours toward circularity.

7. A system in accordance with claim 5, wherein said non-reflective surface areas are sized, shaped, and located to reduce the light intensity differential between any two points on the face panel equi-distant and opposingly located from the face panel center.

8. A system in accordance with claim 5, wherein said non-reflective surface areas are surface-frosted areas.

9. For use in a lighthouse exposure system for exposing, withan appropriate source of actinic light, photosensitive material on a television picture tube face panel, collimator means, comprising a main body portion and a tip portion, for collecting light from said source and for focusing at least part of said collected light by a process of internal reflection from the surface boundary of the main body portion to the tip portion which simulates a point source of light and transmits light towards the face panel, said collimator body including on its surface at least one area which precludes light incident thereon, which would normally be reflected into the tip portion, from reflecting to the tip, such that light intensity patterns formed on said face panel are shaped in a predetermined pattern.

10. A collimator as defined in claim 9 wherein said collimator body surface areas comprise surface-frosted areas. 

1. For more uniformly exposing photosensitive material on a television picture tube face panel using a panel-irradiating source whose uncorrected, panel impinging contours of constant intensity light are improperly configured for picture tube manufacturing purposes, a lighthouse exposure system providing on the face panel corrected contours of constant light intensity without the need for light intensity contour correcting devices disposed between said source and said face panel, said exposure system comprising: means for supporting a television picture tube face panel; an elongated source of actinic light energy; a collimator for focusing the light by reflection from its surface boundary to a simulated point source from which light is transmitted towards said face panel, said collimator having a central optical axis; and means for correcting the constant intensity light contours impressed on said face panel, said means consisting of: at least one predetermined non-reflective surface area on the collimator configured to define a non-circular pattern of nonreflectivity about said optical axis so as to affect said light in a manner which varies as a function of rotational angle about said optical axis, and said surface areas having a predetermined angular relationship with respect to said elongated light source.
 2. A system in accordance with claim 1, wherein said non-reflective surface areas are sized, shaped, and located to modify the constant intensity light contours toward circularity.
 3. A system in accordance with claim 1, wherein said non-reflective surface areas are sized, shaped, and located to reduce the light intensity differential between any two points on the face panel equi-distant and opposingly located from the face panel center.
 4. A system in accordance with claim 1, wherein said non-reflective surface areas are surface-frosted areas.
 5. For more uniformly exposing photosensitive material on a television picture tube face panel using a simulated point source of light whose uncorrected, panel impinging contours of constant intensity light are improperly configured for picture tube manufacturing purposes, a lighthouse exposure system providing on the face panel corrected contours of constant light intensity without mechanically modifying the point source physical embodiment, said exposure system comprising: means for supporting a television picture tube face panel; an elongated source of actinic light energy; a collimator for focusing the light by reflection from its surface boundary to a small tip which simulates a point source and transmits light toward said face panel; a light shield through which only said tip projects and which masks the face panel from all other parts of the collimator; and means for correcting the constant intensity light contours impressed on said face panel, said means consisting of: at least one predetermined non-reflective surface area on the collimator, said areas being located on the collimator portion which is masked from the face panel by said light shield, and said areas being positioned in predetermined alignment with said elongated light source.
 6. A system in accordance with claim 5, wherein said non-reflective surface areas are sized, shaped, and located to modify the constant intensity light contours toward circularity.
 7. A system in accordance with claim 5, wherein said non-reflective surface areas are sized, shaped, and located to reduce the light intensity differential between any two points on the face panel equi-distant and opposingly located from the face panel center.
 8. A system in accordance with claim 5, wherein said non-reflective surface areas are surface-frosted areas.
 9. For use in a lighthouse exposure system for exposing, with an appropriate source of actinic light, photosensitive material on a television picture tube face panel, collimator means, comprising a main body portion and a tip portion, for collecting light from said source and for focusing at least part of said collected light by a process of internal reflection from the surface boundary of the main body portion to the tip portion which simulates a point source of light and transmits light towards the face panel, said collimator body including on its surface at least one area which precludes light incident thereon, which would normally be reflected into the tip portion, from reflecting to the tip, such that light intensity patterns formed on said face panel are shaped in a predetermined pattern.
 10. A collimator as defined in claim 9 wherein said collimator body surface areas comprise surface-frosted areas. 